Sensing technology includes a technique of scanning a given area of an object using an observation sensor including a motor system. A motor of the motor system is controlled to rotate at a target rotational angular speed, maintaining synchronization between a reference signal and a reference angle of a rotating body.
FIG. 8 shows a conceptual diagram showing the operation of scanning a given area of an object using an observation sensor including a rotating body (load) attached to a motor. In the motor system of FIG. 8, a rotating body 202 attached to a motor 203 rotates at a constant target rotational angular speed (steady target rotational angular speed) in the direction indicated by the dotted arrow in FIG. 8. Generally, the direction in which the rotating body 202 faces, that is, the orientation angle of the rotating body 202 (the solid arrow and the dashed arrow in FIG. 8) is specified by the angle from a reference direction. A reference angle is an angle (the solid arrow in FIG. 8) when the rotating body 202 is oriented to a specific position 303 of a scan area 302 of an object 301.
FIG. 9 shows one system to control a motor that drives a rotating body to rotate at a target rotational angular speed. FIG. 9 is a block diagram showing a structure of a motor system with a constant sampling period. In FIG. 9, the motor system includes a scanning unit 201, a clock generation unit 205, an interrupt signal generation unit 207, and a control unit 209.
The scanning unit 201 includes a rotating body 202 that rotates at a steady target rotational angular speed and a motor 203 that drives the rotating body 202. The scanning unit 201 detects a rotational angle 204 of the motor 203 and outputs it to the control unit 209. Further, the scanning unit 201 controls the motor 203 so that the rotating body 202 rotates at a target rotational angular speed by a command value 211 output from the control unit 209.
The clock generation unit 205 generates a clock 206 that serves as the basis for system operation and outputs it to the interrupt signal generation unit 207.
The interrupt signal generation unit 207 counts the clock 206 input from the clock generation unit 205 up to a specified number and thereby generates an interrupt signal 208, and then outputs it to the control unit 209.
To the control unit 209, a target rotational angle 210 for controlling the motor 203 of the scanning unit 201 is input from the outside, and the rotational angle 204 is input from the scanning unit 201. Then, each time the interrupt signal 208 is input from the interrupt signal generation unit 207, the control unit 209 generates the command value 211 for making the rotational angle 204 follow the target rotational angle 210 and outputs it to the scanning unit 201.
In the motor system of FIG. 9, the control unit 209 generates the command value 211 and outputs it to the scanning unit 201 upon receiving the interrupt signal 208 that occurs with a constant sampling period. The motor 203 of the scanning unit 201 is controlled based on the command value 211, so that the rotating body 202 achieves a desired rotational angular speed and is oriented to a specific position of a scan area of an object.
As a technique to control the rotational angular speed of a rotating body to be synchronized with an external reference signal, Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2005-351981) discloses a technique of changing a control gain in accordance with a phase difference between an external reference signal and a reference angle. Patent Literature 2 (Japanese Unexamined Patent Application Publication No. 2006-050717) discloses a technique of generating a motor control signal based on rotational speed control and phase control in accordance with a phase difference between an external reference signal and a reference angle.